A variety of work machines can be equipped with tools for performing a work function. Examples of such machines include a wide variety of loaders, excavators, tele-handlers, and aerial lifts. A work vehicle such as backhoe loader may be equipped with a first tool, such as a backhoe bucket or other structure, for excavating and material handling functions. A swing frame pivotally attaches to the vehicle frame at a rear portion of the vehicle, a backhoe boom pivotally attaches to the swing frame, a dipperstick pivotally attaches to the backhoe boom, and the work tool pivotally attaches to the dipperstick about a backhoe bucket pivot. A vehicle operator controls the orientation of the first tool relative to the dipperstick by a first tool actuator. The operator also controls the rotational position of the boom relative to the vehicle frame, and the dipperstick relative to the boom, by corresponding actuators. The aforementioned actuators are typically comprised of one or more double acting hydraulic cylinders and a corresponding hydraulic circuit.
During a work operation with a backhoe bucket, such as lifting or excavating material, it is desirable to maintain an initial orientation relative to gravity to prevent premature dumping of material, or to obtain a constant excavation shear angle. To maintain the initial backhoe bucket orientation relative to gravity, the operator is required to continually manipulate the backhoe bucket command input device to adjust the backhoe bucket orientation as the backhoe boom and dipperstick are moved during the work operation. The continual adjustment of the backhoe bucket orientation, combined with the simultaneous manipulation of a backhoe boom command input device and a dipperstick command input device inherent in movement of the backhoe boom and dipperstick, requires a degree of operator attention and manual effort that diminishes overall work efficiency and increases operator fatigue.
A loader boom is pivotally attached to the vehicle frame at a front portion of the backhoe loader and a second tool, such as a loader bucket, is pivotally attached to the loader boom at a loader bucket pivot. Work operation with a loader bucket entails similar problems to those encountered in work operations with the backhoe bucket.
A number of mechanisms and systems have been used to automatically control the orientation of work tools such as backhoe and loader buckets. Various examples of electronic sensing and control systems are disclosed in U.S. Pat. Nos. 4,923,326, 4,844,685, 5,356,260, 6,233,511, and 6,609,315. Control systems of the prior art typically utilize position sensors attached at various locations on the work vehicle to sense and control tool orientation relative to the vehicle frame. Additionally, the inventors' patent, U.S. Pat. No. 6,609,315, makes use of an angular velocity sensor attached to the tool to sense and maintain a fixed work tool orientation relative to an initial tool orientation, independent of vehicle frame orientation. The invention, described and claimed herein, makes use of a tilt sensor that, when attached to an object, such as the tool, detects the object's inclination with respect to the earth. The inclination of the tool is detected independently of the vehicle frame orientation and independently of the initial orientation of the tool. The result is a simpler control system and improved tool orientation control relative to gravity.
The particular type of tilt sensor utilized in the invention makes use of a new micro-electromechanical structures (MEMS) technology and is commercially available from Crossbow International, Inc. A number of other tilt sensors, including those utilizing capacitive technology, would be suitable for use in the invention and are also commercially available.